Doctors diagnose the infection by identifying the protozoa in a sample of the infected tissue.

Antiparasitic drugs can control but not eliminate the infection.

Several species of Microsporidia cause infection in people, but symptoms occur mainly in those with AIDS or other disorders that weaken the immune system. These protozoa may infect the intestine, biliary tract, cornea, muscles, respiratory tract, urinary tract, and, occasionally, the brain. The infection may spread throughout the body.

Microsporidia spread through spores, which can be ingested or inhaled or enter through the eye. They may spread from person to person or through contact with an animal. Inside the body, the spores pierce a cell and inject it with material that becomes spores. The cell eventually ruptures, releasing the spores. The spores then spread throughout the body, causing inflammation, or are excreted in the breath, stool, or urine.

Symptoms and Diagnosis

Symptoms vary depending on which species causes the infection and how well a person's immune system is working. People with a normal immune system typically have no symptoms, but microsporidiosis can cause chronic diarrhea in people with AIDS. Other symptoms may include abdominal pain, jaundice, fever, weight loss, a persistent cough, pain in the side (flank), muscle aches, headache, nasal congestion, and eye irritation with redness. Vision may be blurred. If infection is severe, blindness may result.

To diagnose microsporidiosis, doctors examine a sample of the affected tissue under a microscope, usually using special techniques to make the protozoa more visible. Samples of stool, urine, blood, sputum, cerebrospinal fluid (taken by spinal tap), cornea (taken by scraping), or other tissue (taken by biopsy) may be needed.

Treatment

If the immune system is normal, treatment is rarely needed. If it is not, albendazoleSome Brand NamesALBENZA or fumagillin, taken by mouth, may help control but does not eliminate the infection. Eye drops containing albendazoleSome Brand NamesALBENZA and fumagillin may relieve eye symptoms. If they do not, surgery to repair the cornea (keratoplasty) may be required. In people with AIDS, antiretroviral drugs can lessen symptoms.